The Influence of Intensity and Laser-Energy Fluence in Unimolecular Reactions Induced by Monochromatic Infrared Radiation (URIMIR)

Abstract

It has been shown [1] that under certain conditions (not always!) the excitation and reaction processes in URIMIR can be described to a good approximation by a master equation (1) for coarse grained level populations of the molecules:

$$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{\dot p} = \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{K} \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{p} $$

((2))

In the simplest case (Pauli master equation, cases A and B of [1]) the off diagonal rate coefficients for excitation in K are proportional to the laser intensity. Due to the limitations of space we shall restrict our attention here to this case and to the most fundamental kinetic quantity, the overall rate coefficient for the unimolecular reaction defined by (2):

$$ - {\text{dln }}{{\text{F}}_{\text{R}}}/{\text{dt = }}{{\text{k}}_{{\text{uni}}}}({\text{t}})$$

((2))

F_R = 1-F_p is the fraction of remaining reactant molecules at time t. In general k_uni will depend on time, but at steady state we have -k_uni (st.) =λ₁, the largest eigenvalue of the matrix K.